Energy transfer for gcse homework

[andymc]

Can anyone help please or point me to a text I can use to help my daughter
Thanks
Andy

[mep]

Watts to joules calculation formula
The energy E in joules (J) is equal to the power P in watts (W), times the time period t in seconds (s):
E(J) = P(W) × t(s)
So
joules = watts × seconds
or
J = W × s
Example
What is the energy consumption of an electrical circuit that has power consumption of 30 watts for time duration of 3 seconds?
E(J) = 30W × 3s = 90J

from here
http://www.rapidtables.com/convert/electric/Watt_t...

[SystemParanoia]

300 / 60 = 5

50 / 60 = 0.8333

0.8333 * 5 = 4.1w

am i right

[meb90]

1 Watt is 1 Joule of energy transferred in 1 second. The triangle equation is power (Watts) = energy (Joules) / time (s).

So for the question, you have the power and time, energy being power x time. 50W x 300s is 15,000J.

Does the BBC Bitesize website help?
http://www.bbc.co.uk/schools/gcsebitesize/science/...

Edited for school boy maths error...

Edited by meb90 on Friday 17th February 21:16

[andymc]

Is it not 50x300?

I'm well out of practice

[Einion Yrth]

I don't want to appear a completely unreasonable 2@, but this is a question that tests her on stuff that she has been taught. Perhaps she might learn to pay attention?

[mep]

andymc said:

Is it not 50x300?

I'm well out of practice

Yes, it's 50x300 so 15,000J

[andymc]

And next pls

[andymc]

She maintains it's been a supply teacher who is rarely on time, they're all struggling, I'll speak to the school
Andy

[SystemParanoia]

andymc said:

She maintains it's been a supply teacher who is rarely on time,

For the past 5 years ?

[andymc]

She's 13

[thebraketester]

Energy is like magnets. No one knows how they work.

Edited by thebraketester on Friday 17th February 21:34

[SystemParanoia]

andymc said:

She's 13

Mine are 11 ... I really need to swat up so i can keep up and help them. ive forgotten soooooo much

[andymc]

I did this at gcse ages ago, I now sell cars for a living so we all know how well I stuck in

[anonymous-user]

the answers are in the questions though, it is straightway forward maths.

[andymc]

What equation do I use?

Thanks

[MiniMan64]

For both answers just multiple the two numbers in the questions.

First one, power = work / time and you've been given power and time so work = power x time = 15kJ

Second one, energy used to change state = latent heat x mass so 2,300,000 x 0.018

[meb90]

Similar to the previous question.

The specific latent heat means it takes 2.3 x 10^6 Joules to convert 1 kg of water to steam. You have 0.018 kg of water.

0.018 x 2.3 x 10^6 = 41,400.

So 41,400J are needed to convert 0.018 kg or water to steam.

[MiniMan64]

andymc said:

What equation do I use?

Thanks

power (W) = Energy Transferred (J) / Time (s)

Energy Transfered (J) = latent heat x mass (kg)

If she's 13 she's on the new spec and they don't get given those equations for the exam, she'll have to remember them come Year 11.

Try these pages:
Question 1 - http://www.bbc.co.uk/education/guides/zssk7ty/revi...
Question 2 - http://www.bbc.co.uk/schools/gcsebitesize/science/...

[andymc]

Thanks for all the help